International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.4, 163-174 http://ecoevopublisher.com/index.php/ijmec 1 66 and growth, enabling efficient energy transfer in the deep sea (Aguzzi et al., 2018; Dasgupta et al., 2024). It is worth noting that the duration of this stage varies among different whale species. Whales with high fat content and large body size (such as blue whales) have more soft tissue, and their meat accumulation stage may be relatively prolonged and gather more large scavengers. The soft tissues of smaller or leaner whales (such as small toothed whales) are consumed more quickly, and the meat accumulation stage is shorter (Li et al., 2022; Xie et al., 2023). 3.2 Enrichment opportunist stage When the soft tissues of the whale are exhausted and the large scavengers disperse, the whale fall enters an opportunistic stage. This stage lasts for several months to several years and is characterized by the proliferation and growth of a large number of small and medium-sized benthic invertebrates in the sedimentary environment rich in organic matter (Bolstad et al., 2023). The organic debris and fat that seep out during the decomposition of whale carcasses significantly enrich the surrounding seabed sediments, forming a nutrient "halo". Opportunistic species (often organisms that tolerate or even prefer organic enrichment) will settle in large numbers here (Xie et al., 2023). Typical opportunistic organisms include some small polychaetes (such as worms of the Hirudinidae family and sarcandelids, etc.) and crustaceans (such as isopods, amphipods), as well as small bipedal mollusks among mollusks (Bolstad et al., 2023; Xie et al., 2023). They multiply rapidly by taking advantage of the excessive organic debris in the sediment, with individual density and biomass rising sharply in a short period of time, forming high-density communities. It is reported that the density of polychaetes worms in the sediments within a 1-meter radius around whale falls can increase by tens of times compared to the background value (Onishi et al., 2020; Li et al., 2022; Ibrahim et al., 2024). 3.3 Sulfophilic stage The energy transformation stage is the most remarkable and longest-lasting stage in the ecological succession of whale fall, which can last for decades to hundreds of years (Xie et al., 2023). The core of this stage is that the abundant lipids in whale bones decompose and release reducing chemicals such as hydrogen sulfide under the action of anaerobic bacteria, thereby establishing a chemoautotrophic ecosystem similar to cold seeps and hydrothermal fluids (Silva et al., 2021; Pearson et al., 2023). Specifically, the fat rich in whale bone undergoes anaerobic decomposition (sulfate reduction) in the bone marrow buried in sediment, generating a large amount of sulfides that exudate from the bone surface and the surrounding sedimentary environment (Fujiwara et al., 2007; Li et al., 2022). At this stage, numerous peculiar creatures that were unique to whale falls or shared with cold seeps/hot fluids emerged. Among them, the most representative one is the "bone-eating worm" - the tube worm of the Osedax genus. Osedax has no gastrointestinal tract. Instead, it buries into bones through a root-like structure and acquires the products of bone fat decomposition from symbiotic bacteria to nourish itself. Since their first description in 2004, more than 30 species of Osedax have been discovered worldwide. They are landmark species in the fossil energy stage of whale fall (Shimabukuro and Sumida, 2019; Eilertsen et al., 2020). Whale falls have formed miniaturized energy ecosystems similar to cold seeps and hydrothermal vents in the deep sea, which are called "whale fall cold seeps" by some scholars (Danise et al., 2016; Xie et al., 2023). 3.4 Poor nutrition stage (Reef Stage/Decay Stage) When the energy substances in whale bones are almost exhausted, the whale fall ecosystem enters the final oligotrophic stage, also known as the decaying reef stage (Xie et al., 2023). At this point, the main body of the whale bone has been eroded and perforated by a large number of organisms, leaving very little organic matter and reducing the supply of sulfides to levels close to the background. Whale bone remains more often act as hard substrate "reefs", providing a surface for deep-sea benthic organisms to attach to and inhabit. At this stage, chemosymbiotic organisms gradually disappeared, replaced by some filter-feeding or attached later settlers. For example, suspended feeding groups such as sponges, barnacles, corals, and polyps may attach to bare skeletons, while migratory barnacle hermit crabs, small polychaetes, etc. move around the skeletons (Danise et al., 2014; Bolstad et al., 2023).
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